Ultimate Response of Composite Cylinders Under Flexural Load

Composite cylinders are generally used as primary load carrying structures. Their constitutive behavior up to failure is crucial for a critical design. This paper focuses on the ultimate flexural strength of a polymer based composite cylinder subjected to bending. In such a case, the outmost filament of the cylinder subjected to the maximum bending stress fails the first. The complexity, however, lies in the fact that the failure of this outmost filament generally does not correspond to the ultimate failure. Additional loads can still be applied to the cylinder and a progressive failure process will result. To deal with such a problem in this paper, the cylinder is discretized into a number of lamina layers with different widths. The bridging micromechanics model [Huang, Z. M., Composites Part A, 2001] combined with the classical lamination theory has been applied to understand the progressive failure process generated in the cylinder. Only its constituent fiber and matrix properties under bending are necessary for this understanding and reasonably good accuracy has been achieved. However, the ultimate failure of the cylinder cannot be figured out only based on a stress failure criterion, as one cannot know a priori which ply failure corresponds to the ultimate failure. An additional critical deflection (curvature) condition must be employed also. By using both the stress and the deflection conditions, the estimated ultimate strength of the cylinder agreed well with an experimental measurement.